Latch for drill bit control apparatus



Aug. 12, 1969 W. R. GARRETT LATCH FOR DRILL BIT CONTROL APPARATUS FiledAug. 3l, 1967 4 Sheets-She y /3 fl?? Aug. 1.2, 1969 W. R, GARRETT3,460,639

LATCH FOR DRILL BIT CONTROL APPARATUS Filed Aug. 31, 1967 4 Sheets-$heet2 W//a nr Ga fr e f! INVENTOR.

W. R. GARRETT LATCH FOR DRILL [31T CONTROL APPARATUS Aug. l2, 1969 4Sheets-Sheet 5 Filed Aug. 31, 1967 W////am f?. Gar/'eff I NVENTQR.

Aug. l2, 1969 w. R. GARRETT 3,460,639

LATCH FOR DRILL BIT CONTROL APPARATUS Filed Aug. 51, 19e? 4 Sheets-Sheet4 W//am R. G arr e INVISNTOR.

United States Patent O 3,460,639 LATCH FOR DRILL BIT CONTROL APPARATUSWilliam R. Garrett, Midland, Tex., assignor to Smith IndustriesInternational, Inc., a corporation or California Filed Aug. 31, 1967,Ser. No. 664,878 Int. CI. E21b 17/10, 7/04; E21c 9/00 U.S. Cl. 175-23010 Claims ABSTRACT F THE DISCLOSURE The hydraulic guide lbarrel for adrill bit mandrel is releasably latched to mandrel in lower position ofbarrel on Imandrel by a latch pin radially reciprocable in mandrel intoand out of engagement with a slot in the barrel. The pin is positivelydriven lby a cam which reciprocates axially in barrel in response topredominating of Vtwo forces, namely, an upward -force provided by ahelical compression spring and a downward force provided by iluid in themandrel acting against piston connected to cam.

CROSS REFERENCES TO RELATED APPLICATIONS BACKGROUND OF THE INVENTIONField of the invention This invention pertains to apparatus useful inboring holes in the earth, especially petroleum wells. The apparatus isluseful to guide the bit so that the hole will proceed in the desireddirection.

Description of prior art According to the prior art, as exemplified bythe aforementioned Garrett et al. patent, the guide barrel is latched tothe lbit mandrel by a pin radially reciprocable in the mandrel into andout of engagement with a slot in the barrel, as `shown in FIGURE 9 ofsaid patent. The latch is freely reciprocable in the mandrel and urgedoutwardly into engagement with the barrel slot by fluid pressuredifferential, e.g. when `the apparatus is in use with the slush pump inoperation maintaining a higher fluid pressure inside the mandrel than inthe well bore annulus outside the mandrel. However with the pump on, therbarrels hydraulic shoes are propelled into engagement with the wellwall to anchor the barrel in the hole, and upon downward motion of themandrel in drilling the barrel pushes against the beveled side of thelatch pin and forces it inwardly so that relative motion -of mandrel andbarrel can proceed. When the downward travel of the mandrel relative tothe barrel reaches its limit, the mandrel is elevated until the latchpin is in position to engage the slot in the barrel. Thereupon lluidpressure in the mandrel causes the latch to move out into engagementwith the slot in the barrel. The pump is then turned oit and -theresiliently mounted wall engaging shoes of the barrel retract, therebyfreeing the barrel. At the same time a lock member, axially reciprocablein the mandrel and normally held down by fliuid pressure but blasedupwardly 'by a helical compressing spring, moves into position behindthe latch pin to prevent its moving inwardly, The barrel can then bepositively moved downward in the hole -by moving the mandrel down, thelock preventing the barrel from `overriding the latch pin. When the`barrel is lowered to the desired level, the pump is turned on again toactivate the -barrel shoes into wall engagement. At lthe same time thefluid pressure in the mandrel acts against a piston carried by the lockto force the lock downwardly against the force of the compressionspring, thereby unlocking the latch pin so that on downward movement ofthe mandrel the barrel can ride `over the latch pin.

In the foregoing construction, it: will `be observed that in order toeffect positive latching of the mandrel to the barrel it is necessaryrst to turn the pump on to move the latch pin into position andthereafter to turn the pump off to position the lock behind the pin.When the pump is turned yon again after repositioning of the Ibarrel hashas been completed `and drilling is to proceed, the fluid pressurecreated lby the pump moves the barrel shoes out to anchor the barrel andmoves the lock out from behind the latch pin, but the latch pin remainsin engagement with the barrel slot. llt is necessary for the barrel toride over the pin in order for driling to proceed.

The primary object of the present invention is to provide a latchactuating means that will positively retract the latch from barrelengagement whenever the fluid pressure differential is at the levelcorresponding to drilling operations, e.g. when the pump is on, and willpositively extend the latch into barrel engagement whenever the fluidpressure differential falls below that level, e.g. when the pump is off.This simplified operation of the latch provides greater reliability, asis highly essential in apparatus of this kind.

SUMMARY OF THE INVENTION According to the invention a cam is axiallyreciprocably mounted in the mandrel. The cam is biased upwardly by ahelical compression spring and is connected to a piston which moves itdownwardly under ruid pressure differential. The cam engages a latch pinradially reciprocatable in the mandrel into and `out of engagement withthe barrel slot. FIlhe cam and latch pin are positively engaged, thelatch pin passing through a slot` in the cam.

The cam has a small slot through which the body connecting the followerportions of the latch pin may pass and also a larger slot through whichthe follower portions and tail ends of the latch pin can be passed.Therefore the latch pin can be made as an integral member.

rPhe latch pin extends clear across the mandrel bore so that both endsof the latch pin are supported in bores in the mandrel.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURES 1 and 2 are axial sectionsthrough apparatus embodying the invention;

FIGURES 3 and 4 are elevations of the alignment spears of the apparatusshown in FIGURES 1 and 2;

FIGURE 5 is an elevation of the cam and guides of the apparatus shown inFIGURES 1 and 2;

FIGURES 6 and 7 are elevations of the latch pin of the apparatus shownin FIGURES 1 and 2;

FIGURE 8 is an elevation of a drill bit control apparatus in which theinvention is incorporated; and

FIGURES 9 and l0 are sections taken at planes 9 9 and 10-10 of FIGURE 8.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGURES 1 and 2there is shown a tubular steel mandrel 10 and a tubular steel barreltherearound including a main body portion 11 and an alignment spearportion 12 screw connected to the main portion at the lower end thereof.Packing 13 lheld between the spear and body portions of lthe barrelforms a seal between the barrel and mandrel at the lower end of thepressurized annular chamber 14 therebetween. An internally iluted rubbersleeve bearing 15 secured inside the barrel supports the mandrel forrelative rotation and reciprocation. Since the upper ends of the barreland mandrel are the same as described in the aforementioned Garrett etal. patent, no further description thereof need be given, referencebeing made to said Garrett et al. patent for a further and fullerdescription thereof.

An alignment spear is screw connected to the mandrel. As shown inFIGURES 3 and 4, the alignment spears 12 and 20 are simply steel tubeshelically out off at angle to the axis forming spear tips 21, 22. Thehelicoidal form of the spear surfaces is described in more detail insaid Garrett at al. patent. The base of each spear is provided with ashort slot as shown at 23, 24, the ends of the slots being rounded asshown at 25, 26. The barrel spear is further provided with a slot 27 atits side 180 degrees removed from tip 21. As best shown in FIG- URE 2the ends of the slot 27 are beveled as shown at 28, 29, flaring inwardlytoward the axis of the barrel and mandrel.

Referring now to FIGURE l the threaded pin 39 of a drill bit 40 isscrewed into the lower end of the mandrel. A fluid ow responsive unit 41comprising a check valve and a cam actuating means is disposed insidethe mandrel between the upper end 42 of the rock bit pin and adownwardly facing beveled shoulder 43 in the mandrel. The cam actuatingmeans includes a steel sleeve 44 having a beveled upper end 45 adaptedto engage the shoulder 43. The lower end 46 of sleeve 44 is internallythreaded to receive the threaded tupper end 47 of the steel body 48 ofthe check valve 49.

A pair of arms 50, only one of which appears in the drawing, extenddownwardly from valve body 48 to base ring 51. A spacer ring 52 is screwconnected to the base ring, the spacer ring resting against opper end 42of drill 40.

The check valve 49 includes a valve seat 53 having an elastomeric sealring 54 emplaced therein and protruding beyond the valve seat. A steelring 55 is pressed inside the seal ring to hold it in place.

A valve closure 56 is pivotally connected to the valve body at 57, andis urged to closed .position by a torsion spring (not shown) coaxialwith the pivot shaft.

The purpose of the cheek valve is to prevent upward flow of uid in thedrill bit 40 and the bit control apparatus when the drill string isbeing lowered into the well bore through the drilling fluid, e.g. liquidor mud. Whenever there is no fluid pressure differential acting upwardlyon the valve closure 56, the torsion spring holds it in closed positionagainst the force of gravity. If there is down ow of liquid through thevalve, the closure 56 opens and may vibrate slightly. There is anelastomer disc 58 bonded to the upper face of the closure to cushion thecontact thereon of the tubular steel piston rod 59 when the latter isextended below valve seat 53. Without the rubber disc 58, the closure 56may be destroyed by fretting in the course of a few hours.

The piston rod 59, forming part of the cam actuation means, extendscoaxially inside sleeve 44. Near the upper end of the piston rod 59there is a piston 60 comprising an annular external rib 65 against whichis shouldered a steel ring 66 of T cross-section. A steel piston body 67is secured to the rod 59 between T ring 66 and a steel split snap ring67 received in groove 68 in the piston rod. An elastomer O-ring 69 ingroove 70 in the piston body seals the body to the rod. The outerperiphery of the body includes la hemi-toroidal portion 72. Around theouter periphery of the piston body, snapped over the hemitoroidalenlargement thereof, is an elastomeric seal ring 4 73 having double lipseals 74, 75, 76, 77 at each end thereof. The hemi-toroidal portion ofthe piston body provides a partial back up for the seal ring 73.

In FIGURE l, the piston comprising body 72, seal ring 73, T ring 65,snap ring 67', and O-ring 69, is shown at the upper limit of its travel,the snap ring 67 bearing against steel stop ring 80. Ring is heldbetween shoulder 81 in the sleeve 44 and a steel snap ring 82. The stopring includes a neck 83 which contacts the snap ring 67. The main bodyof the stop` ring is provided with a plurality of ports as shown at 88.The piston moves axially within enlarged bore 89 of the sleeve 44. Thedownward travel of the piston is limited 'by upwardly facing shoulder 90which engages the lower surface 91 of the outer periphery of the T ring65.

Tlhe tongue 95 of the T ring bears against the upper end of steelzhelical compression spring 96. The lower end of spring 96 bears againstthe top of flapper valve 49, there lbeing a spring seat 97 lfonmed atthe bottom of the threaded neck 47. The spring is disposed coaxiallyaround the piston rod 59 inside sleeve 44. The spring 96 urges thepiston upwardly to the limit of its travel. The spring is preloaded sothat it bears against the lpiston with considerable upward 'force evenwhen the piston is at the upper limit of its travel.

A choke 100 made of tungsten carbide is secured in the lower end ofthetubular piston rod between downwardly facing shoulder 101 and a steelsnap ring 102 received in groove 103 in the piston rod. The pressuredifferential across choke 100, piston rod 59, and piston 60 existingwhen fluid -is being pumped through the man-drel is designed to be greatenough to overcome the force of spring 96 and :move the pistondownwardly to the lower limit of its tnavel.

It is to be observed that when fluid is flowing down the mandrel, theclosure 56 of the check valve will be in open position and there isample room for the piston rod 59 to move through the valve seat as thepiston 60 moves to the lower limit of its travel.

The cam actuating means comprises sleeve 44, spring 96, spring seat 97,piston 60, piston rod 59, stop ring 80, and choke 100. The cam actuating[means actuates oam means which in turn actuates latch means forconnecting the mandrel 10 tothe barrel 11, 12.

The cam means 110, shown in FIGURES 2 and 5 comprises a bar 111 havinggenerally at parallel vertical sides 112, 113. Near the ends of the barthe sides 112, 113, are connected by cylindrically curved outerperipheral guide surfaces 114, 115, 116, 117 adapted to slide on theinner periphery 118 of mandrel 10 as the cam means reciprocatescoaxially therein. The space between the Hat sides of the bar and theinner periphery 118 of the manidrel -provides space for uid low in themandrel past the lbar.

The lower and |upper ends of the bar are cut back away from the innerperiphery 118 of the mandrel to provide cylindrically curved seats 119,120, 121, 122 to receive cylindrically curved tongues 123, 124, 125, 126extending from the upper end of the tubular piston rod 59 and the lowerend of tube 127 of an orienting instrument receiver. Seat 122 and tongue126 are shorter than the other seats rand tongues to insure correctorientation of the receiver with respect to the bar during assembly. Thetongues are fastened to the seats by roll pins 128 driven thnough holesin the tongues and through holes 129 the ends of the bar between theseats. The pins iit loosely in the tongues so that the cam means willnot bind inside the mandrel due to misalignment.

The orienting instnument receiver 130 comprises a steel tube adapted toreciprocate axially within the mandrel, being provided with guideiblocks 140, 141 Welded to its outer periphery to center the tube 127within the mandrel. Within the tube 127 is an alignment key 142 formedintegral with one of the guide blocks 140 yand extending through a slotin tube 127.

The upper ends ot the guide portions 150, 151 of the bar 111 and of theupper end 152 of the bar are beveled as shown at 160, 161, 162, 163,164, 165, 166, 167, 168 to streamline these portions of the bar relativeto downward flow of drilling iluid such as air, gas, water, or mud,which may be used in the drilling process.

Between the guide portions 150, 151 the bar 111 is cut at an angle tothe cylinder axis of the lguide portions to form front and back camsurfaces 170, 171. The cam body 172 between surfaces 170, 171 isprovided with a slot 173 extending from near the yguide portion 150 atthe lower end of the bar 111 upwardly toward the guide portion 151 nearthe upper end of the bar. The upper end of the slot merges with a largerslot 175 adjacent upper guide portion 151. The part 176 of bar 111around slot 175 is of `greater thickness than that between at surfaces112, 113 defining the thickness of the remainder of the bar. Theenlarged part 176 is beveled at 177, 178 to merge smoothly with theremainder of the bar. To facili- .tate assembly with the steel latch pin180, the back side of the bar adjacent enlargement 17 6 is relievedbelofw the plane dened by rear cam surface 171, as shown at 179.

Referring now to FIGURES 2, 6, and 7, the front end of the latch pin 180is adapted to reciprocate in a bushed aperture in the mandrel providedby bushin-g 181 received in bore 182. The back end of the latch pin isslidab'ly supported 4in cylindrical socket 183 bored in the mandrel 10.The latch pin 180 is a bar having flat vertical parallel sides 185, 186and cylindrically curved upper and lower surfaces 187, 188. The back endof the latch pin is bevefled as shown at 189, 190. The curved surfaces187, 188 slide on the inner surface of bushing 181 and inside socket 183as the latch pin reciprocates forward and backward relative to barrelslot 27. The chisel point 192 formed by bevels y189, 190 cuts throughany detritus accumulated in the socket and forces it out through thespace between ats 185, 186 and the interior of socket 183.

The thickness of the latch pin 180 between sides 185, 186, is slightlyless than the width of slot 175 in the cam bar 111 so that the latch pincan be passed through slot 175. A threaded hole 193 in the front end ofthe latch pin is adapted to receive a handling tool to facilitateinsertion of the latch pin through mandrel bushing 181 and cam slot 175into mandrel socket 183. This assembly is accomplished when the cam slot175 is in alignment with the socket and bushing. To effect such assemblythe barrel is moved along the mandrel to a position such that the barreldoes not cover bushing 181 in the mandrel. The ow responsive unitcomprising the `check valve actuating means can be lowered whenever thedrill bit 40 is not connected to the mandrel, and by lowering the flowresponsive unit the cam slot 175 can be brought into alignment with themandrel bushing and socket.

Near the lmidportion of the latch pin, there is a thin section 200connecting the `front and back ends ofthe latch pin. The thin portionhas flat parallel sides 201, 202. Shoulders 203, 204, 205, 206 at thejunctures o'f the fiat sides 185, 186 with at sides 201, 202 provide thefollower surfaces of lthe latch pin. These sides are inclined to thehorizontal or cylinder axis of the latch pin at an angle x which isequal to the angle of inclination to the vertical of mandrel axis ofcarn surfaces 170, 171. The perpendicular distance lbetween the `frontfollower surfaces 203, 204 and the back follower surfaces 205, 206 isslightly larger than the perpendicular ydistance between the front andback cam surfaces 170, 171, so as to make a loose sliding lit therewith.

During assembly, after the latch pin has been passed through bushing 182and cam slot 175 into socket 191, the cam bar 111 is elevated. The thinconnecting portion 200 of the latch pin enters the -thinner slot 173 inthe cam bar 111, the cut away portion 179 on the back side ot the cambar facilitating entry of cam surfaces 170, 171 between the lfollowersurfaces olf the latc-h pin. Once the drill bit has been screwed intothe mandrel, the cam bar can no longer be lowered suiciently to alignslot with the latch pin, so that the latch pin is positively retained bythe cam bar.

'Ilhe front end of the latch pin is of circular cross section, includinga cylindrical guide portion 210 slidably mounted in the bushing 181. Thebushing (see FIG. 2) has a flange 212 on its inner end supported byinwardly facing shoulder 213 between bore 182 and a counter bore 215 inthe mandrel 10. The bushing is inserted through one end of the mandreland pushed out against shoulder 213. An elastomer O-ring 216 (see FIG.6) in annular groove 217 on the latch pin, seals the latch pin to thebushing.

The outer extremity or -tip 220 of the latch pin is coni cally tapered,flaring inwardly. This facilitates entry of the latch pin into slot 27.It also helps cam the latch pin inwardly should it not be Ifullyretracted and the barrel need to ride over it.

The operation of the apparatus is simple. When drilling has proceeded tothe limit of the downward travel of the mandrel 10 in the barrel, themandrel is elevated to the upper limit of its travel. The pump is thenshut off lowering the fluid pressure in the mandrel. This not onlyreleases the hydraulic shoes of the anchor barrel from engagement withthe wall of the well bore but allows spring 86 to `drive the cam bar 111upwardly, forcing latch pin 1-80 into slot 27. The mandrel is thenlowered, carrying the barrel down the well bore to a new |lowerposition. The pump is then turned on, causing iiuid pressure in themandrel to` increase. This not only moves the hydraulic shoes of theanchor barrel to wall engaging position, but it drives the piston,piston rod, and choke downwardly. Downward movement of the piston rodmoves the cam bar 111 downward, positively retracting Rlatch pin fromslot 27. The motion of the latch pin is thus synchronized with that ofthe hydraulic shoes of the anchor barrel.

The overall operation of the invention with reference to the entire bitcontrol 'apparatus may be more fully understood by reference to FIGURES8, 9 and 10. As shown in FIGURE 8, the bit control apparatus includesmandrel 10 adapated to be screw connected to the lower end 249 (eg. atool joint or sub) of a drill string by means of threaded pin 250.Axially and rotatably slidable on the mandrel is the barrel includingspear portion 12, lower seal portion 251, lower bearing portion 252,anchor portion 253, middle bearing -portion 254, middle seal 255, upperbea-ring 256, and detritus seal 257. A port 258 in the mandrel opensinto the pressurizable annular chamber or space 14 around the mandrelinside the barrel between the lower seal and middle seal. The alignmentspears 12, 20 rotate the barrel into predetermined azimuthal positionrelative to the mandrel whenever the spears are brought into engagementby elevating the mandrel relative to the barrel. Mandrel spear 20 andthe sub 249 limit relative yaxial travel of the barrel and mandrel sothat port 258 is always in communication with chamber 14.

Referring also to FIG. 9, there are a plurality of steel anchor shoes260 radially reciprocatably mounted in the barrel. Elastomer seals 261bonded to the shoes and to steel retaining rings 262 normally hold theshoes in retracted position, the rings having outwardly facing shoulders263 bearing against inwardly facing shoulders 264 in the apertures 265in the barrel. If desired, the bonded elastomer seals may be replaced bvsliding -seals so that the shoes are not biased toward retractedposition but are merely movable to retracted position under externalmechanized or huid pressure. Fluid pressure inside the mandrel exceedingthat outside the barrel will extend the -anchor shoes into engagementwith the wall 270 of the well bore. The shoes are asymmetricallydisposed around the barrel to push the barrel and mandrel to one side ofthe hole as determined `by the azimuthal 7 positioning of the barrel.Upon drop in pressure the elast-omer seals retract the anchor shoes.

Referring also to FIGURE 10, latch pin 180 is seen to be extended intobarrel slot 27. When uid pressure rises in the mandrel to extend theanchor shoes, the latch pin 180 will at the same time be retracted. Whenthe mandrel pressure drops, retracting the anchor shoes, the latch pinwill at the same time Ibe extended, provided the mandrel is positionedrelative to the barrel to permit such extension. If not so positioned,the latch pin will remain retracted, acting backwards through the cam toprevent the spring 86 from moving cam bar 111 upwardly. Then as soon asthe latch pin and slot come into register, the latch pin will beextended by the cam bar moving under the `force of the spring.

Whenever the latch pin 180 is in slot 27, not only can the barrel bemoved up and down in the well bore with the mandrel to Ithe desiredelevation but it can also be rotated to the desired azimuthal position;the alignment spears orienting the barrel relative to the mandrel andthe mandrel orientation being known from a surveying instrument loweredthrough the drill string and oriented in receiver 127 by key 142.

While a preferred embodiment yof the invention has been described, manymodifications thereof can be made by one skilled in the art withoutdeparting `from the spirit of the invention.

I claim:

1. Drill bit control apparatus including a tubular mandrel adapted to beconnected in a drill string, a barrel disposed around the mandrelaxially and rotatably slidable relative thereto, upper and lower sealmeans between the mandrel and barrel spaced apart axially defining theupper and lower ends of -a pressurizable annular chamber around themandrel inside the barrel, means limiting the axial travel of the barrelrelative to the mandrel, port means placing the interior of the mandrelin communication with the annular chamber in all positions of the barreland mandrel within the limits of relative axial travel thereof, anchorshoe means radially reciprocably disposed in said barrel and extensibleunder pressure of uid transmitted to `said chamber from said mandrel,and latch means extendible from the mandrel into engagement with thebarrel to prevent relative motion therebetween, said drill bit controlapparatus being distinguished by the inclusion of means lfor retractingsaid latch means from engagement with the barrel in response to uidpressure in said mandrel in synchronism with the extension of saidanchor shoe means thereby.

2. Subject matter of ella-im 1 further distinguished by said latchretraction means including cam means engaged with said latch means andfluid pressure responsive means for actuating said cam means.

3. Subject matter of claim 2 further distinguished by said latohretraction means also serving as latch extension means. said cam meansbeing movable between a position positively extending said latch meansand a position positively retracting said latch means, said fluidpressure responsive means moving said cam means from one position to the`other according to the iluid pressure in said mandrel.

4. Subject matter of claim 3 further distinguished by said iluidpressure responsive means including piston means acting to move said cammeans to latch retracting position and spring means acting to move saidcam means to latch extending position.

5. Subject matter of claim 4 further distinguished by said cam meansincluding a lbar axially reciprocable in said mandrel, said bar havingguide surfaces correlative to and cooperable with the inner periphery ofsaid mandrel and having parallel cam surfaces inclined at au acute angleto the axis of the mandrel, said latch means ihaving parallel followersurfaces cooperating with said cam surfaces and inclined at the sameangle to the axis of said mandrel.

6. Subject matter of claim 5 further distinguished by said latch meanshaving a thin connecting portion between said portions thereof lhavingsaid `follower surfaces, said cam bar having a slot therethroughdividing each of said cam surfaces into a pair of coplanar surfaces,said connecting portion of said latch means being slidably disposed insaid slot.

7. Subject matter of claim 6 wherein said mandrel includes 1an apertureand said barrel includes a slot, said apparatus being furtherdistinguished by said mandrel having a socket opposite said aperture,said latch means comprising a pin having a front end reciprocable insaid aperture into and o'u't of said slot land having a back endreciprocable in said socket.

8. Subject matter of claim 7 further distinguished by said cam barhaving a second slot therethrough connected to but larger than the firstmentioned slot therethrough, said second slot being large enough topermit passage of said back end of the latch pin therethrough, said backend of the pin being too large to pass through the irst slot whereby tolock said pin in said cam bar when said pin is in said first slot.

9. Subject matter of claim 7 lfurther distinguished by said socket beingcylindrical and said back end of the latch pin including cylin-dricallycurved surfaces cooperating with said socket, said pin having surfacesrelieved below the cylindrical surfaces thereof to provide ilow passagesbetween the socket and back end of the pin, the tip of the Iback end ofthe pin being beveled to a ohisel point.

10. Subject matter of claim 4 further distinguished by said iiuidpressure responsive means including `a tubular steel piston rod, saidspring means being ooaxially disposed around said rod, said piston meansbeing connected to the upper end of said rod, said piston rod having achoke disposed in its lower end, said spring means and piston rod landpiston means being `disposed inside a sleeve ooaxially mounted in saidmandrel and sealed thereto, said piston means being adapted toreciprocate within and seal with said sleeve, said apparatus including acheck valve connected to the lower end of said sleeve, said check valveincluding a pivotally mounted closure, said closure having anelastomeric covering over its surface adjacent said sleeve to reducefretting upon contact therewith of said piston rod when extended throughsaid valve by fluid pressure in said mandrel.

References Cited UNITED STATES PATENTS 2,179,567 11/1939 Strength 175-732,316,409 4/ 1943 Downing 175-73 2,819,040 l/1958 James et al -763,042,125 7/1962 Duncan 175-73 3,105,561 10/1963 Kellner 175-2303,326,305 6/1967 Garrett 175-230 X CHARLES E. OCONNELL, Primary ExaminerRICHARD E. FAVREAU, Assistant Examiner U.S. Cl. X.R. 175-81

